Roller screw mechanism

Abstract

A roller screw mechanism including a screw provided with an outer thread, a nut surrounding and coaxial with the screw, the nut being provided with an inner thread, a plurality of rollers radially disposed between the screw and the nut and each provided with an outer thread and with two outer gear teeth two gear wheels each provided with gear teeth meshing with the gear teeth of the rollers, and two spacer rings for maintaining the rollers circumferentially spaced apart. The spacer rings are axially offset towards the inside relative to the gear teeth of the gear wheels.

1 . A roller screw mechanism comprising:
 a screw having an outer thread,   a nut surrounding and coaxial with the screw, the nut being provided with an inner thread,   a plurality of rollers radially disposed between the screw and the nut and provided with an outer thread engaging the outer and inner threads and with two outer gear teeth,   two gear wheels each provided with gear teeth meshing with the gear teeth of the rollers, and   two spacer rings for maintaining the rollers circumferentially spaced apart, and wherein   the spacer rings are axially offset towards the inside relative to the gear teeth of the gear wheels.   
     
     
         2 . The roller screw mechanism according to  claim 1 , wherein each spacer ring is axially located between the outer thread of each roller and one of the outer gear teeth of the roller. 
     
     
         3 . The roller screw mechanism according to  claim 2 , wherein each spacer ring includes a plurality of recesses radially open inwardly and axially open on both sides. 
     
     
         4 . The roller screw mechanism according to  claim 3 , wherein each roller provides an outer groove axially located between the outer thread and each outer gear teeth, each groove of the rollers being located in one of the recesses of each spacer ring. 
     
     
         5 . The roller screw mechanism according to  claim 4 , further comprising two elastic retainer rings each mounted in a groove provided on the associated spacer ring in order to radially hold therebetween the rollers into the recesses of the spacer ring. 
     
     
         6 . The roller screw mechanism according to  claim 5 , wherein the gear wheels are mounted in a non-threaded part of the nut. 
     
     
         7 . The roller screw mechanism according to  claim 6 , wherein each spacer ring is radially disposed between the outer thread of the screw and the associated gear wheel. 
     
     
         8 . The roller screw mechanism according to  claim 7 , wherein each spacer ring is mounted into a bore of the associated gear wheel extending the gear teeth. 
     
     
         9 . The roller screw mechanism according to  claim 5 , wherein the gear wheels are provided on the screw. 
     
     
         10 . The roller screw mechanism according to  claim 9 , wherein each roller provides, at each axial end, an end frontal surface oriented axially outwards and delimiting axially the associated outer gear teeth. 
     
     
         11 . The roller screw mechanism according to  claim 10 , wherein the gear teeth of the rollers and the gear teeth of the gear wheels each have in cross-section an involute profile. 
     
     
         12 . The roller screw mechanism according to  claim 11 , wherein the gear teeth of the rollers and the gear teeth of the gear wheels each have in cross-section a circular arc-profile. 
     
     
         13 . The roller screw mechanism according to  claim 12 , wherein the gear teeth of the rollers and the gear teeth of the gear wheels each have in cross-section a hypocycloid profile. 
     
     
         14 . An actuator comprising:
 a rotating means and   a roller screw mechanism, the screw of the mechanism being coupled with the rotating means, the screw mechanism having;
 a screw having an outer thread, 
 a nut surrounding and coaxial with the screw, the nut being provided with an inner thread, 
 a plurality of rollers radially disposed between the screw and the nut and provided with an outer thread engaging the outer and inner threads and with two outer gear teeth, 
 two gear wheels each provided with gear teeth meshing with the gear teeth of the rollers, and 
 two spacer rings for maintaining the rollers circumferentially spaced apart, and wherein 
 the spacer rings are axially offset towards the inside relative to the gear teeth of the gear wheels.